Communication terminal devices may directly communicate with base stations in a cellular communication system. All end devices of a centralized group communication system must be connected to the central group communication server. End devices that are only connected to a single other end device of a centralized group communication system cannot communicate with the rest of the group. Furthermore, communication terminal devices that are also provided with a short range wireless transceiver may serve as a relaying device to the base station for other communication terminal devices. The other communication terminal devices may also be communicating with the cellular mobile communication system via a short range wireless transceiver and the communication terminal device, even without being in direct connection with a base station of the cellular mobile communication system. If an end device simply relays communication data from a group communication server to another end device then communication data would be sent twice to the relaying end device. This unnecessarily would consume communication resources. And, if an end device simply relays communication data from another end device to a group communication server then relayed communication data from the other end device would be sent back to the relaying end device from the server. This unnecessarily would consume communication resources, too.